1. Field of the Invention
The present invention relates to a liquid discharge head which includes discharge ports to discharge liquid droplets and separate liquid chambers connected to the discharge ports and in which a displacement is applied to a vibration plate disposed to face each separate liquid chamber and constituting a part of the chamber to thereby discharge the liquid droplets, and a manufacturing method of the liquid discharge head. The liquid discharge head of the present invention is applicable to a recording unit which prints information on paper, cloth, leather, nonwoven cloth, OHP sheet or the like, a patterning unit which attaches a liquid to a solid such as a substrate or a plate material, a coating unit or the like.
2. Description of the Related Art
Liquid discharge heads have heretofore been incorporated broadly in recording units such as a printer and a facsimile machine for reasons such as a low noise, a low running cost and ease of miniaturizing and coloring of a unit. Especially, the liquid discharge head using a piezoelectric actuator enlarges its application as a patterning unit for device manufacturing owing to a high degree of freedom in selecting a liquid to be discharged.
There will specifically be described a process in which the liquid is discharged from discharge ports in the liquid discharge head using the piezoelectric actuator. First, an electric signal is supplied to thereby apply a displacement which changes with time to a vibration plate constituting a part of each separate liquid chamber, thereby contracting or expanding a volume of the separate liquid chamber. When such a volume control is performed, the liquid having a liquid column state starts to extend and protrude to the outside. Subsequently, while a plurality of liquid droplets are separated from one another by a surface tension, the droplets fly through, for example, a gap between a recording head (the liquid discharge head) and a recording material. On the other hand, in the application as either the recording unit or the patterning unit, achievements of a high resolution of nozzle arrangement and a micro amount of the discharged liquid droplets are advanced. Moreover, increase of a liquid droplet shot precision is achieved. Above all, as a main method of increasing the resolution, decreasing of a width of the separate liquid chamber is investigated.
In a case where the width of the separate liquid chamber is decreased to thereby increase the resolution, a displacement efficiency needs to be improved in order to realize desired discharge performances such a discharge amount and a discharge speed. To solve the problem, as a measure, decreasing of a thickness of the vibration plate is known (see Japanese Patent Application Laid-Open Nos. H11-291495 and H11-300971).
However, as a result of specific investigations of the present inventor, the following technical problems have been clarified in a case where the thickness of the vibration plate is decreased as much as possible.
An investigation object is a unimorph type (a vendor type) piezoelectric recording head in which the vibration plate is provided with piezoelectric articles as piezoelectric driving sections and electrodes. Several types of piezoelectric recording heads are prepared by changing the thickness of each vibration plate to compare discharge lives. Here, as a criterion for judging the life, a time when the vibration plate cracked is regarded as a liquid leak generation time in a vibration plate portion, and the life is evaluated by the number of discharge operations up to that time. As easily expected, the thinner vibration plate has a shorter life owing to the crack of the vibration plate.
Moreover, when a displacement amount of the vibration plate is measured in a longitudinal direction of a separate liquid chamber in one element of the unimorph type piezoelectric recording head, the following tendency is observed.
FIG. 8 is a sectional view of the unimorph type piezoelectric recording head. A separate liquid chamber 105 has a length of 2.5 mm. When a voltage is applied to a piezoelectric element 106, a vibration plate 107 deforms. FIG. 9 plots the displacement amount of the vibration plate 107 in the longitudinal direction of the separate liquid chamber at a certain time after the voltage is input.
Curves T1, T2 and T3 show that the vibration plate 107 deforms, when time t elapses to t1, t2 and t3. However, it is seen that the displacement amount of the vibration plate 107 largely fluctuates at opposite end regions of the separate liquid chamber 105, that is, in the vicinity of a discharge port 102 and at an end portion on a common liquid chamber side as compared with another place.
When the displacement amount of the vibration plate peculiarly fluctuates more largely at the end portions on a discharge port side and the common liquid chamber side than in another large region, destruction or crack of the vibration plate easily occurs at the end portions. It has been seen that the vibration plate end portions on the discharge port side and the common liquid chamber side further easily crack especially in a case where the vibration plate is thinned.